1. Field of the Invention
The present invention relates to a method of dividing a wafer, provided in its face-side surface with a plurality of streets in a grid pattern and provided with devices in a plurality of regions demarcated by the plurality of streets, along the streets into the individual devices (chips).
2. Description of the Related Art
In the semiconductor device manufacturing process, usually, a plurality of regions are demarcated by planned dividing lines called streets arranged in a grid pattern in a surface of a substantially circular disk-shaped semiconductor wafer, and devices such as ICs and LSIs are formed in the thus demarcated regions. Then, the wafer is cut along the streets, to manufacture the individual devices. Similarly, an optical device wafer in which a gallium nitride compound semiconductor and the like are laminated on a surface of a sapphire substrate is also cut along streets, to be divided into individual optical devices such as light emitting diodes and laser diodes, which are widely utilized for electric apparatuses.
As a method for dividing a plate-shaped work such as a semiconductor wafer, a laser beam machining method has been attempted in which a pulsed laser beam capable of being transmitted through the work is used, and irradiation with the pulsed laser beam is conducted by adjusting the focal point in the inside of the regions to be divided. In a dividing method based on the use of this laser beam machining method, a work is irradiated from one side thereof with a pulsed laser beam having such a wavelength as to be transmitted through the work while adjusting the focal point to the inside of the work, so as to continuously form a denatured layer in the inside of the work along the streets, and an external force is exerted along the streets where strength is lowered due to the formation of the denatured layer, thereby dividing the work (refer to, for example, Japanese Patent No. 3408805).
Besides, there has been proposed a method in which a wafer provided with a denatured layer along streets by the above-mentioned laser beam machining method is adhered to a dicing tape attached to an annular frame, then the dicing tape is expanded, whereby the wafer is divided along the streets where strength is lowered due to the formation of the denatured layer, into the individual devices (refer to, for example, Japanese Patent Laid-open No. 2004-273895).
Meanwhile, the wafer provided therein with the denatured layer along the streets is very susceptible to cracking. Therefore, the wafer may be broken or damaged in a feeding step in which the wafer provided therein with the denatured layer is fed from the laser beam machining apparatus for the purpose of adhering the wafer to the dicing tape, during when the wafer provided with the denatured layer is adhered to the dicing tape and/or in a feeding step in which the wafer adhered to the dicing tape is conveyed to a tape expanding unit.